The Grand Ice Age

Not long ago, one of my Road Trip Interest Group members (you know who you are) asked this question:

“When was the last Ice Age?”

The term “Ice Age” is somewhat ambiguous. Fluctuations in the Earth’s climate are extreme and take place over many periods of time. There have been eras when the Earth was completely devoid of ice. There have been other times when all the Earth’s oceans had completely turned to ice. So, when was the last “Ice Age”?

The most recent time that has been referred to by that name was the “Little Ice Age”(LIA). When exactly that was depends on who you ask. The chart below defines the LIA as being between the years 1400 and 1800 AD. This was a time that saw mountain villages in Europe consumed by glaciers. The “Frost Fairs” on the frozen River Thames in London happened at these times and the story of Hans Brinker, likewise. There is ample evidence of the LIA in art, literature and history. That painting of George Washington un-wisely standing in a rowboat, while his men push big chunks of ice in the Delaware out of the way? LIA, again. Below is a graph of results for last two millenia of proxy derived temperature differences. You see the Little Ice Age as well as what came before.

Timespan: 2000 Years

Figure 1: The Medieval Warm Period (MWP) and the Little Ice Age (LIA).

These are differences in temperatures derived from examination of cylinders of ice drilled out of an ice sheet. Where that zero axis falls depends on how much time is included in the graph. So, these data do not tell us what a thermometer would have said then. But, the historical record tells us that during the Medieval Warm Period (MWP) Greenland was occupied by an agricultural civilization where none at that level of technology would be possible in today’s climate. In Alaska there are glaciers that have retreated from the Little Ice Age and uncovered immense tree-stumps still rooted in the ground. There are no such climax forests there today.

Thousand-year-old tree stump uncovered by the Mendenhall Glacier’s retreat from the Little Ice Age

They date to about one thousand years ago. So, we know for a fact that the temperatures were warmer then than now. There are some who imagine that this was only the case for the North Atlantic. But, Alaska is not on the Atlantic, is it? And ice cores from Antarctica tell pretty much the same story.

The time before the LIA was much warmer than the climate today. The MWP was, itself just another in a series of warm periods, starting with the Minoan Warm Period and occurring roughly every 1000 years. Below is a graph of oxygen-Isotope proxy temperature anomalies.

The last “Ice Age” (without the “Little” modifier) is to be seen at the extreme left of the Holocene graph in figure 2. It is more accurately referred to as a “Glaciation” and is a part of a (roughly) one-hundred thousand-year oscillation of extreme cold followed by short periods (10,000 years or less) of warm weather. This cycle is revealed, among other places – in the Vostok and EPICA Ice Core Projects in Antarctica.

Timespan 450,000 years

Figure 3. Antarctic Ice-core derived temperature differences.

You see that our current situation is an “Interglacial” age called the Holocene Climate Optimum that comes after the “Ice Age” (Glaciation). The Eemian which came before that Glaciation is another Interglacial in a long series of same, stretching back half a million years – at least. The Holocene appears to be significantly cooler than the previous Interglacials – all of them. (Put that in your “Global Warming” pipe and smoke it! 😉 )

While the future is not yet determined, it looks very much like the Holocene is about over and the next Glaciation is soon to be expected.

But, in all of this, there is still ice at the poles and on mountaintops. The Glaciations seem to be the rule and the “Interglacials”, the exceptions. Could we not say that the entire timespan above was a part of a larger “Grand Ice Age” with only the interglacial times interrupting?

What happens if we widen the time span? Below is a graph of ocean sediment-derived temperatures.

Timespan: Five Million Years.

Figure 4. Temperature differences derived from ocean sediments

The fact that those hundred-thousand-year cycles of the previous graph are seen lends credibility to this seafloor sediment “proxy” of temperature. Notice those thousand-century cycles are a recent phenomenon (relatively speaking) and followed a period of 41,000 year cycles. Before that was a much warmer time. There is fossil evidence that those were times when there was little or no ice on Earth at all.

Be warned that they will bring up “Global Warming” even though they can’t point to five-million-year-old Ford Explorers or make any reasonable defense of “Man-made Global Warming”. -Steve

Quote about Antarctica:

“She recalled: “We were high up on glaciated peaks when we found a sedimentary layer packed full of fragile leaves and twigs.”

“These fossils proved to be remains of stunted bushes of beech. At only three to five million years old, they were some of the last plants to have lived on the continent before the deep freeze set in.”